My husband suffered from severe nursing care negligence in a rehab center. What can we do to be compensated for this poor treatment?

My husband had heart surgery and then was sent to a rehab center.. He was there for two weeks and was released and sent home. Home Care nurses discovered the huge area of bed sores and an abscess the day after he arrived home. Four days later he was too weak to even get out of bed. He was sent by abulance to the hospital and remained there for two weeks. He had to have an operation on his abscess that then required a vac wound pump for four more weeks in the hospital and upon his return home. He has been under Home Care nursing up until last week. He has lost 23 pounds and it weak and tired. We blame the rehab center for not turning him in the bed he lay in for two weeks even though he had some few hours a week of rehab exercises some days. What can we do about this sad and unwarranted situation/